13 



frozen and thawed ; the cells forming the tissue are separated 

 from each other and lose their cohesion, instead of being 

 firmly agglutinated together as in their sound state ; and 

 consequently the rasp is unable to tear the cells in pieces, 

 but separates them from each other whole, without allowing 

 the starch they contain to escape. A small number only of 

 the cells are lacerated, and it is they which yield what starch 

 the manufacturer obtains from tliem, a quantity which 

 scarcely amounts to 3 per cent. The principal part of the 

 starch remains locked up in the pulp which is thrown away. 



M. Payen was led incidentally to notice the different 

 proportions of starch lodged in the different parts of a 

 potatoe ; and he found that the smallest quantity exists in 

 the centre, which is separated by a circular row of fibres from 

 the outer part, which is the true bark of the tuber. The 

 latter, or cortical part, which abounds in starch, is divided 

 from the epidermis by a thinner tissue, in which is almost 

 exclusively deposited the acrid and venomous matter of the 

 plant, and which is entirely without starch. 



This observation explained to M. Payen the cause of 

 frozen potatoes being acrid and strong tasted. In their sound 

 state the acrid matter contained in the rind of the potatoe is 

 not mixed with the other fluids of the parenchyma of the 

 tuber ; but when frost has separated the cells of the paren- 

 chyma, the fluid then extravasated flows into their interstices, 

 and the acrid and venomous matter dissolved by them par- 

 takes of the general diffusion ; it is the physical effect of 

 the tendency which fluids placed in contact have to mix with 

 each other. 



Proceeding from these observations M. Payen has ex- 

 amined in what manner frozen potatoes can be turned to 

 some useful purpose. As they have not lost any part of their 

 starch, they ought to preserve, after being thawed, all their 

 alimentary qualities, if they are quickly dried after having 

 been properly prepared. M. D'Orbigny states, that in Peru 

 this mode of preserving potatoes for food is commonly em- 

 ployed. The Peruvians cause the tubers to be frozen on 

 their mountains, and then bring them down into their valleys, 

 where the heat rapidly dries them; and in this state of desic- 

 cation they preserve their nutritive property for an indefinite 

 time. 



It would therefore appear not only that potatoes when 



